For example, a step-up/step-down converter or the like that steps up and down an input voltage includes two-channel control means, and performs the respective feedback controls in a switching manner (see, for example, Patent reference 1). This device is configured to step up or down a power supply voltage to be supplied to a capacitor, a secondary cell or battery and then to perform a power running operation or a regeneration operation. Specifically, it includes a PI control system used to perform a step-up operation and a PI control system used to perform a step-down operation, and these control systems are connected to a power output means or the like in a switching manner to perform the respective device operations described above. In addition, some of the devices that perform two-channel feedback control perform continuous control while switching between, for example, constant current control and constant voltage control.
FIG. 4 is an explanatory diagram illustrating a configuration of a conventional PI control device. This figure illustrates an example configuration of a PI control device 101 that performs feedback control (PI control) on a control object 111 such as, for example, a capacitor.
The PI control device 101 includes the following elements as a current control system: a reference input unit (A) 102 that receives an input of a set current value from outside, a current control unit 103 that performs PI control using this set current value, and a current measurement unit (A′) 104 that measures the current flowing through the control object 111.
The PI control device 101 further includes the following elements as a voltage control system: a reference input unit (B) 105 that receives an input of a set voltage value from outside, a voltage control unit 106 that performs PI control using this set voltage value, and a voltage measurement unit (B′) 107 that measures the voltage generated in or being applied to the control object 111.
An output point of the current control unit 103 and an output point of the voltage control unit 106 are connected to an output control unit 108 via a changeover switch 109. The changeover switch 109 is connected to a switching determination unit 110 that determines switching between the aforementioned current control and voltage control in accordance with, for example, the voltage output of the control object 111 or the like.
The output control unit 108 includes, for example, a power semiconductor element, and is configured to output a voltage or current having a magnitude corresponding to a control signal (output voltage) or the like output from the current control unit 103 or the voltage control unit 106 to the control object 111.
The current control unit 103 includes a subtractor 201 that determines a difference between the respective output values of the reference input unit (A) 102 and the current measurement unit (A′) 104, a P control unit 202 that determines a P control value using the output value of the subtractor 201, an I control unit 203 that determines an I control value using the output value of the subtractor 201, and an adder 204 that adds together the respective output values of the P control unit 202 and the I control unit 203 to determine a PI control value.
The voltage control unit 106 includes a subtractor 205 that determines a difference between the respective output values of the reference input unit (B) 106 and the voltage measurement unit (B′) 107, a P control unit 206 that determines a P control value using the output value of the subtractor 205, an I control unit 207 that determines an I control value using the output value of the subtractor 205, and an adder 208 that adds together the respective output values of the P control unit 206 and the I control unit 207 to determine a PI control value.
FIG. 5 is an explanatory diagram illustrating a configuration of a conventional PID control device. An illustrated PID control device 120 has a similar configuration to the PI control device 101 in FIG. 4, except for a current control unit 121 and a voltage control unit 122.
The current control unit 121 includes a subtractor 201, a P control unit 202, an I control unit 203, and an adder 204, and further includes a D control unit 210 that determines a D control value using the output value of the subtractor 201. The adder 204 of the current control unit 121 is configured to add together the respective output values of the P control unit 202, the I control unit 203, and the D control unit 210 and to output a PID control value.
The voltage control unit 122 includes a subtractor 205, a P control unit 206, an I control unit 207, and an adder 208, and further includes a D control unit 211 that determines a D control value using the output value of the subtractor 205. The adder 208 of the voltage control unit 122 is configured to add together the respective output values of the P control unit 206, the I control unit 207, and the D control unit 211 and to determine a PID control value.
Next, the operation will be described.
The PID control device 120 in FIG. 5 operates in a manner similar to the PI control device 101, except that it controls the control object 111 using values including the respective output values of the D control units 210 and 211, and the operation of the PI control device 101 will thus be representatively described here. In addition, the charging operation on the control object 111 will be exemplarily described. In the following, control switching is performed in a similar manner even if charging is substituted with discharging.
When a set current value is input to the current control unit 103 from outside through the reference input unit (A) 102 in the manner described previously, the current control unit 103 determines, using the subtractor 201 included therein, the deviation of the measured value of the current flowing through the control object 111, which current is output from the current measurement unit (A′) 104, from the aforementioned set current value, and the resulting value is input to the P control unit 202 and the I control unit 203. The respective values determined by the P control unit 202 and the I control unit 203 are added together using the adder 204 to determine a PI control value (current control value).
Further, when a set voltage value is input to the voltage control unit 106 from outside through the reference input unit (B) 105, the voltage control unit 106 determines, using the subtractor 205 included therein, the deviation of the measured value of the voltage across, for example, electrodes of the control object 111, which is output from the voltage measurement unit (B′) 107, from the aforementioned set voltage value, and the resulting value is input to the P control unit 206 and the I control unit 207. The respective values determined by the P control unit 206 and the I control unit 207 are added together using the adder 208 to determine a PI (Integral) control value (voltage control value).
FIG. 6 includes explanatory diagrams illustrating the operation of the PI control device in FIG. 4. These figures illustrate a control operation when the switching determination unit 110 controls the changeover switch 109.
FIG. 6(a) illustrates the change in charging current supplied from the PI control device 101 to the control object 111 over time, with the vertical axis representing current values and the horizontal axis representing elapsed time.
FIG. 6(b) illustrates the change in, for example, the inter-electrode voltage of the control object 111 connected to the PI control device 101 over time, with the vertical axis representing voltage values and the horizontal axis representing elapsed time.
FIG. 6(c) illustrates the change in current control over time when a charging current is supplied to the control object 111 as described above, with the vertical axis representing current control values and the horizontal axis representing elapsed time. Note that, in FIG. 6(c), the P control value (graph (1)) output from the P control unit 202 and the I control value (graph (2)) output from the I control unit 203 are illustrated in terms of current control values.
FIG. 6(d) illustrates the change in voltage control over time when the charging current described above is supplied (a charging voltage is applied), with the vertical axis representing voltage control values and the horizontal axis representing elapsed time. Note that, in FIG. 6(d), the P control value (graph (3)) output from the P control unit 206 and the I control value (graph (4)) output from the I control unit 207 are illustrated in terms of voltage control value.
In a case where the control object 111 is, for example, a lithium-ion secondary cell or battery and a charging current is to be supplied to the control object 111, the switching determination unit 110 controls the changeover switch 109 to connect the current control unit 103 and the output control unit 108 when charging begins. The current control unit 103 connected to the output control unit 108 performs PI control so that a charging current to be supplied to the control object 111 becomes equal to the set current value input from the reference input unit (A) 102.
In this case, the current control unit 103 determines the deviation of the measured current value measured by the current measurement unit (A′) 104 from the set current value described above, and adjusts the current control value, which is determined by P control and I control as illustrated in FIG. 6(c), to perform constant current control (PI control) so that the subsequent measured current values are set equal to the set current value and maintained constant.
As described previously, when, with the progress of charging by constant current control, as illustrated in FIG. 6(b), the voltage value of the control object 111 increases and reaches the set voltage value input by the reference input unit (B) 105, the switching determination unit 110 determines that a switching condition occurs at an illustrated point P1, and switches the connection of the changeover switch 109 to connect the voltage control unit 106 and the output control unit 108.
In other words, for example, when the measured voltage value of the voltage measurement unit (B′) 107 reaches the set voltage value, the switching determination unit 110 switches from constant current control, which has just been performed, to constant voltage control at a point P2 in FIG. 6(c).
When the voltage control unit 106 is connected to the output control unit 108 by the control switching described above, it determines a voltage control value for keeping the inter-electrode voltage of the control object 111 constant in a manner as depicted in a constant voltage control period illustrated in FIG. 6(b).
Immediately after the switching determination unit 110 has performed switching from constant current control to constant voltage control, the voltage control value output from the voltage control unit 106 is unstable in a manner depicted at a point P3 (varying period) illustrated in FIG. 6(d) and particularly the voltage control value determined by I control markedly varies, making the voltage or the like being supplied to the control object 111 unstable.